Expandable intervertebral implant

ABSTRACT

An expandable intervertebral implant includes a front wall, a back wall spaced apart from the front wall, and two side walls connecting the front wall and the back wall at their respective ends. The walls define a space. The implant further includes a bottom face, a top face, at least one engagement member with an engagement surface for engagement with the end plate of a vertebral body, a first adjusting element and a second adjusting element which are supported by a first support member and a second support member, respectively, and which cooperate with the respective support member such that the engagement member is reciprocally movable between a first end position and a second end position. In the first end position, the engagement surface does not project beyond the bottom face or the top face and in the second end position, the engagement surface at least partially projects outwardly beyond the bottom face or the top face. The first and the second support members are coupled by a coupling mechanism.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation of U.S. patent applicationSer. No. 11/944,580, filed Nov. 23, 2007, which claims the benefit ofU.S. Provisional Patent Application Ser. No. 60/860,944, filed Nov. 24,2006, and claims priority from European Patent Application EP06024332.6,filed Nov. 23, 2006, the entire disclosures of which are incorporatedherein by reference.

BACKGROUND

The present application generally relates to intervertebral implants,and more particularly, to an expandable intervertebral implant.

An intervertebral implant is inserted after removal of an intervertebraldisk for stabilizing the intervertebral region until bone material whichis filled in at the same time has grown to an osseous connection andstrengthening.

An expandable intervertebral implant is known from U.S. Pat. No.6,176,882 B1. The intervertebral implant comprises two spaced sidewalls, a front wall connecting the side walls at one end thereof, a backwall connecting the side walls at the other end, the walls defining acorresponding space within the walls, a bottom face, a top face, eachface extending transversely to said walls, at least one engagementmember disposed within the space defined by said walls, said engagementmember having a surface oriented toward one of the bottom face or thetop face, and two wedge members which are supported in the front walland the back wall by a threaded spindle having two ends and two portionswith opposite thread pitches, one end of the threaded spindle beingrotationally supported in the front wall and the other end beingrotationally supported in the back wall. The two wedge members aresupported within the space in such a manner that, upon rotation of thethreaded spindle in one direction, a distance between the wedge membersdecreases and, upon rotation of the threaded spindle in an oppositedirection, the distance between the wedge members increases. The wedgemembers operate to move the engagement member reciprocally. The outercontour of the expandable intervertebral implant is rectangular.Therefore, the wedge members can be supported on one single threadedspindle.

Another expandable intervertebral implant is known, for example, from WO2005/058209 A2. The implant includes a body having a longitudinal axisand including first and second axial walls spaced apart along atransverse axis, first and second transverse end walls extending betweenand interconnecting the first and second axial walls. The intervertebralimplant includes an expansion member co-acting with the axial walls toexpand the body along the transverse axis. The outer contour of theimplant in a plane parallel to the end plates of the vertebral body isalso rectangular. An intervertebral implant with a rectangular contourdoes not fit perfectly to the shape of the end plates of the vertebralbody. For certain applications an anatomically-shaped intervertebralimplant is desired.

US 2005/0125062 discloses a height adjustable intervertebral implantwhich has an anatomical shape.

Based on the above, there is a need to provide an expandableintervertebral implant which allows a facilitated insertion and at thesame time has an improved simple handling of the expansion mechanism.

SUMMARY

The disclosure relates to an expandable intervertebral implantcomprising a front wall, a back wall and a two side walls connecting thefront wall and the back wall, the walls defining a cavity having an openbottom and top, and at least one member movable in the cavity from afirst position wherein its surface does not project out of the cavityand a second position wherein its surface at least partially projectsout of the cavity. The implant is actively expandable from either of twosides. Further, the implant has an anatomical shape.

The intervertebral implant is anatomically-shaped, in particular, it hasa banana-shape or a kidney-shape. However, due to the expansionmechanism of the intervertebral implant according to the invention, itcan be easily adapted to have any other shape which is even more adaptedto the natural shape of the end plate of the vertebral bodies.

The intervertebral implant can be expanded by accessing it from eitherside.

Various coupling mechanisms can be used to couple the rotational motionof one support member which serve for expanding the implant to the othersupport member.

Further features and advantages of the invention will become apparentand will be best understood by reference to the following detaileddescription of embodiments taken in conjunction with the accompanyingdrawings.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of the intervertebral implantaccording to a first embodiment.

FIG. 2 shows a perspective front view of the assembled intervertebralimplant of FIG. 1.

FIG. 3 shows a perspective top view of the intervertebral implant ofFIGS. 1 and 2 with the upper engagement member omitted.

FIG. 4 shows a detail of FIG. 3 in an enlarged view, partly in section.

FIG. 5 shows the drive mechanism of the implant shown in FIG. 3.

FIG. 6 shows a perspective front view of a coupling member of thecoupling mechanism shown in FIG. 5.

FIG. 7 shows a top view of the coupling member of FIG. 6.

FIG. 8 shows a side view of the coupling member of FIG. 6.

FIG. 9 shows another side view of the coupling member of FIG. 6.

FIG. 10 shows a perspective view of the implant according to FIGS. 1 and2 with a modified coupling mechanism and the upper engagement memberbeing omitted.

FIG. 11 shows a detail of the modified coupling mechanism.

FIG. 12 shows a side view of the coupling mechanism shown in FIG. 11.

FIG. 13 shows a perspective top view of another modified couplingmechanism.

FIG. 14 shows a top view of the member of FIG. 13.

FIG. 15 shows a side view of an engagement member of the implant in afirst embodiment.

FIG. 16 shows a perspective top view of the engagement member of FIG. 15

FIG. 17 shows a perspective bottom view of the engagement member of FIG.15.

FIG. 18 shows a perspective view of an outer portion of the engagementmember of FIG. 15.

FIG. 19 shows a side view of an engagement member of the implantaccording to a second embodiment.

FIG. 20 shows a perspective top view of the engagement member of FIG.19.

FIG. 21 shows a front view of the expandable intervertebral implant withthe engagement members in a retracted position.

FIG. 22 shows a front view of the expandable intervertebral implant withthe engagement members in an expanded position.

FIG. 23 shows an implant partially in section with the engagementmembers of FIG. 19 in the retracted condition.

FIG. 24 shows an implant partially in section with the engagementmembers of FIG. 19 in the expanded position.

FIGS. 25 a to 25 e show steps of assembling the intervertebral implant.

DETAILED DESCRIPTION

As shown in FIGS. 1 to 7, the expandable intervertebral implant includesa front wall 1, a back wall 2 spaced apart from the front wall, andfirst side wall 3 connecting the front wall 1 and the back wall 2 attheir one end as well as a second side wall 4 opposite to the first sidewall for connecting the front wall and the back wall at their oppositeother ends. As best shown in FIG. 1, the bottom and top faces are openso that the four walls define a cavity 5 having an open bottom and anopen top. The front wall 1 and the back wall 2 have approximately thesame length and are curved in approximately the same direction. The sidewalls 3 and 4 are shorter and connect the front wall 1 and the back wall2 in such a way that a substantially banana-shaped or kidney-shapedcontour is defined by the walls. The length and the curvature of therespective front and back wall and the side walls can be selected so asto be adapted to the size and shape of the opposing end plates of thevertebral bodies between which the implant is to be inserted. The heightof the front wall 1 and the back wall 2 slightly increases towards thecenter of the walls (see FIGS. 21 to 24) in order to be adapted to acorresponding depressed portion of the end plate of the vertebral body.The front wall 1 and the back wall 2 have preferably a plurality ofapertures 6 which have a diamond shape in the embodiment shown. However,the shape of the apertures 6 can also be circular, oval-shaped orotherwise shaped.

As shown in particular in FIGS. 1 and 2, the side walls 3 and 4 comprisebores 7, 7′, respectively, at approximately their center. As can be seenbest in FIG. 4 the bore 7 and the corresponding opposite bore 7′ eachhave a first portion 8 with a first bore diameter adjacent to theoutside of the side wall, respectively, and a following second portion 9which opens into the cavity 5 and which has a second bore diameter whichis slightly less than the first bore diameter. Thereby, the secondportion 9 defines a shoulder.

A bearing member (or bearing journal) 10, 10′, respectively is insertedinto the bore 7, 7′. Each bearing member 10, 10′ has a first cylindricalportion with a first outer diameter and adjacent thereto a secondcylindrical portion with a second outer diameter matching the innerdiameters of the first portion 8 and the second portion 9 of the bore 7,7′, so that the bearing member rests on the shoulder. The size of thebearing member 10, 10′ is such, that the bearing member 10, 10′ is heldin the bore 7, 7′, respectively, by press-fitting.

The implant further comprises two threaded spindles 11, 11′, each havinga first cylindrical end 12, 12′ with a recess 13, 13′, preferably ahexagon recess, at the free end for engagement with a tool (not shown).The outer diameter of the cylindrical first end 12, 12′ is slightlysmaller than the inner diameter of the bearing 10, 10′ so that first end12, 12′ of the spindle can be inserted into the bearing 10, 10′ and canbe rotatably held therein. Each spindle further has a cylindrical secondend 14, 14′, opposite to the first end 12, 12′.

The thread pitches of the threaded spindles 11, 11′ are opposite to eachother. The length of the threaded spindles is such that when thespindles are held in the bearings 10, 10′ and project into the cavity 5,the second ends 14, 14′ of the spindles do not touch each other.

As can be seen in particular in FIGS. 3 to 5 the threaded spindles 11,11′ are connected with the second ends 14, 14′ via a coupling member 15.The coupling member 15 in the embodiment shown in FIGS. 1 to 7 isdesigned as a curved tube portion having slits 16 extending in acircumferential direction. The slits are offset from each other in sucha way that the slits of one circumferential line cover at least suchportions of an adjacent circumferential line, where no slit is provided.The inner diameter of the coupling member 15 is such that the couplingmember 15 can be connected to the cylindrical end portions 14, 14′ ofthe threaded spindles for example by means of a press-fit connection.The curvature and length of the coupling member is such that it isadapted to the angle α which the longitudinal axis L, L′ of the threadedspindles 11, 11′ enclose with each other. Accordingly, the curvature ofthe coupling member 15 corresponds substantially to the curvature of thefront wall 1 and the back wall 2 of the implant. The number, width andlength of the slits 16 are selected so as to provide a desired bendingflexibility to the tube while providing sufficient torsional stiffness.

As can be seen in FIG. 3 a circular flange 17, 17′ can be provided atthe end 14, 14′ of each spindle 11, 11′ to provide a stop the functionof which will be described later. The flange 17, 17′ has a projection 18on opposite sides which rests on a shoulder 19 provided at the innerside of the front wall 1 and the back wall 2, respectively. The flange17, 17′ also provides for a guidance and/or support for the spindles andthe coupling member.

As can be seen in particular in FIGS. 1 and 3, to 5 a wedge member 20,20′ is provided on each threaded spindle 11, 11′. Each wedge member isdefined by a top face 21, 21′ and an opposite bottom face 22, 22′ whichinclude an angle with each other to define the wedge-shape. Each wedgemember 20, 20′ comprises a flat front wall 23, 23′ and a curved rearwall and flat side walls. The flat front wall 23, 23′ and the top wall21, 21′ and the bottom wall 22, 22′ are arranged such that the distanceincreases between top wall and bottom wall in a direction away from thefront wall. The wedge member 20, 20′ comprises a threaded bore having aninternal thread corresponding to the external thread of the threadedspindle 11, 11′, respectively. The wedge members 20, 20′ are screwedonto the corresponding threaded spindles 11, 11′ in such a position thattheir corresponding top faces 21, 21′ and bottom faces 22, 22′ areinclined towards each other. As can be seen in particular in FIG. 3, theback walls of the wedge members are curved in such a way that they fitto the curvature of the inner side of the side walls 3, 4 of theimplant.

As shown best in FIGS. 1, 2 and 15 to 18, a first engagement member 30and a second engagement member 30′, respectively, is placed between themutually inclined top faces 21, 21′ and mutually inclined bottom faces22, 22′, which will be referred to as wedge faces, of the wedge members20, 20′. Each engagement member 30, 30′ has on its lower face facing thewedge members two mutually inclined sloping surfaces 31, 32 and 31′,32′, respectively. The angle of inclination of the surfaces 31, 32 and31′, 32′, respectively, corresponds to the wedge angle of the wedgemembers. Between the left and right inclined surfaces 31, 32 and 31′,32′, the engagement member 30, 30′ comprises a substantially curvedcylindrical recess 33, 33′ which is sized so as to be able toaccommodate the coupling member 15 including the flanges 17, 17′. Therecess 33, 33′ runs out into the inclined surfaces 31, 32 and 31′, 32′,respectively. The inclined surfaces of the engagement members 30, 30′and the wedge faces of the wedge members 20, 20′ can slide onto eachother. To enhance the sliding capability, the faces can be coated with acoating or can be polished.

As can be seen in particular in FIGS. 16 and 17, the contour of theengagement members is approximately banana-shaped or kidney-shaped andcorresponds to the contour of the implant body as shown in FIGS. 1 and2. The top surface 34 of the engagement member 30 has in the embodimentshown a right portion 34 a and a left portion 34 b which have a slightinclination with respect to each other, the inclination being oppositeto the inclination of the inclined surfaces 31, 32 on the lower side.The second engagement member 31′ has a corresponding top surface 34′with inclined portions 34 a′, 34 b′ (not shown). The top surface 34further has an engagement structure 35 which can be designed as teethprojecting from the surface or as ribs or as any other structure whichis suitable for engagement with the surface of the end plates of thevertebral body.

As can be seen in FIGS. 1, 2, 15 and 16, each engagement member 30, 30′comprises a substantially U-shaped slit 36, 36′ extending from the topsurface 34, 34′ to a certain distance therefrom. The front wall 1 andthe back wall 2 each comprise bores 38, 38′ located in the centerbetween the side walls, one in the upper half and one in the lower half.Two pins 39, 39′ extend through opposite bores 38 across the cavity 5.The pins 39, 39′ engage the U-shaped slits 36 of the engagement members30, 30′, respectively. By means of this, a stop is formed preventingfalling-out of the engagement members 30, 30′. The U-shaped slits 36also form a guidance for the engagement members 30, 30′.

The arrangement of the pins 39, 39′ and the depth of the U-shaped slits36, 36′ are matched to each other such that the maximum heights ofoutward movement of the respective engagement members over the bottomface and the top face is determined by the relative position of the pin39, 39′ and the depth of the slits 36.

The dimensions of the wedge members 20, 20′, the threaded spindles 11,11′ and the engagement members 30, 30′ as well as the pitch of thethreads is designed so as to allow the engagement members to bedisplaced from a first position shown in FIGS. 21 and 23 in which thetop surface 34, 34′ is located in the cavity 5 to a second positionshown in FIGS. 22 and 24 in which the top surface 34, 34′ projects abovethe cavity 5 of the implant.

The implant is manufactured from a biocompatible material, such astitanium, a biocompatible plastic material or other biocompatiblematerials. The coupling member 15 is for example manufactured fromstainless steel or titanium to provide sufficient strength.

In operation, first, the wedge members 20, 20′ are brought into theposition shown in FIG. 3 wherein the back walls are in contact with theinner sides of the side walls 34 of the implant by rotating one of thethreaded spindles. This causes each engagement member 30, 30′ to take upits lowermost position wherein the engagement structure 35 of the topsurface 34, 34′ does not project beyond the cavity 5 of the implant. Theimplant can therefore easily be inserted into the area between twovertebrae and there is no risk of injuring the soft parts of the endplates of the vertebrae. Since the contour of the implant isapproximately banana-shaped the insertion is facilitated compared to theinsertion of a rectangular implant. The implant can be inserted in sucha way that the front wall is oriented in the dorsal direction and theback wall is oriented in the ventral direction and the side walls areoriented laterally. The indication of the front, back and side wall doesnot limit the use of the implant to the particular way of insertion andis merely for the distinction of the walls with respect to each other.After having correctly positioned the implant between the vertebrae, thetwo wedge members 20, 20′ are moved towards each other by engaging oneof the threaded spindles 11, 11′ by accessing it from one of the sidewalls 3, 4 with a tool, for example with an Allen wrench engaging therecess 13, 13′ of the spindle. By rotating one of the threaded spindlesthe rotational movement is transferred by the coupling member 15 to theother threaded spindle. In the embodiment shown in FIGS. 1 to 7, thecoupling member 15 has weakened portions at its slits 16 in order toprovide a bending capability with sufficient torsional stiffness whichallows to transfer the rotational motion of one spindle to the otherspindle. By rotating one of the spindles the mutually inclined wedgesurfaces 21, 22 and 21′, 22′ of the two opposed wedge members 20, 20′exert a force onto the inclined surfaces 31, 32 and 31′, 32′ of thecorresponding engagement members 30, 30′ to raise the same until theengagement structure 35 of the top surface 34, 34′ projects out of thecavity 5 to thereby engage the end plates of the respective vertebrae.The lifting movement of the engagement members 30, 30′ is limited by thestop formed by the pins 39, 39′ as particularly shown in FIG. 24. Theflanges 17, 17′ can also provide a stop for the movement of the wedgemembers.

The transmission of the rotation of the tool through one threadedspindle to the other threaded spindle and from the wedge members to theengagement members allows a precise adjustment of the expansion of theengagement members and allows for an individual adaptation of theimplant to the anatomical shape of the end plates of the vertebrae ofthe individual patient.

The threaded spindles prevent the engagement members from becoming looseby themselves. The engagement members 30, 30′ can be retracted only bybackward rotation using a tool whereby the pressure exerted by thevertebrae onto the engagement members forces the engagement members backinto the cavity 5 of the implant. This releases the engagement structurefrom the end plates of the vertebrae.

FIGS. 19 and 20 show an alternative embodiment of the engagement member.The engagement member 300 differs from the engagement member 30, 30′ inthat it has two opposed slanted surfaces 301 a, 301 b adjacent to theU-shaped recess 36 the inclination of which can be parallel to theinclination of the inclined surfaces 31, 32 on the lower side of theengagement member 300. The slanted surfaces 301 a, 301 b do not have anengagement structure. By means of the engagement members 300 of thisembodiment, support is provided at the outer part of the end-plate,where the highest bone strength is provided.

A further modification of the coupling mechanism to transfer therotational movement from one spindle to the other spindle is shown inFIGS. 10 to 12. The coupling mechanism can be formed by a bevel geardrive comprising two pinions 150, 151 engaging each other. Each pinionis non-rotatably connected to the spindles 11, 11′.

A further modified embodiment of the coupling mechanism for transferringthe rotational movement of one spindle to the other spindle is shown inFIGS. 13 and 14. The coupling mechanism includes a flexible tube 160which has a curvature and dimensions similar to the coupling member 15shown in FIGS. 1 to 7 and which is sized so as to be press-fit connectedto the ends 14, 14′ of the spindles. The coupling member 160 transfersthe rotational movement by a deformation of the flexible material. Thecoupling member 160 can be made for example, from nitinol or flexibleplastic material with bending flexibility but torsional stiffness.

FIGS. 25 a to 25 e show steps for assembly of the implant. In the firststep shown in FIG. 25 a, the first spindle with the correspondingwedge-member screwed thereon is inserted into the cavity and thecorresponding bearing. As a next step the coupling member 15 isconnected to the first spindle. Then, the second wedge member isinserted, the second spindle guided through the second bore and screwedthrough the second wedge member until it can be connected with theflange of the coupling member. Then, the second bearing is inserted(FIGS. 25 a and 25 b). As shown in FIGS. 25 c and 25 d, when thespindles including the wedge members are inserted and coupled by thecoupling member the engagement members can be inserted and the pins 39,39′ put through the bores 38, 38′, as shown in FIG. 25 e.

Although the walls are described as front wall, back wall and sidewalls, this is not to be understood as a limitation for the orientationof the implant between the vertebrae. The shape of the implant is notrestricted to a banana shape or kidney shape. For example, the shape canbe ring-shaped or a quarter ring or a half ring or any other shape.

It is also conceivable that more than two wedge members on more than twosupporting members are provided enclosing an angle with each other. Forexample three support spindles enclosing an angle of 120° with eachother and three adjustment or wedge members can be provided.

Other coupling mechanisms are conceivable, for example a corrugatedtube, a cardan joint or a bowden cable. Even non mechanical couplings,for example, a magnetic coupling is possible.

While a particular form of the disclosure has been illustrated anddescribed, it will be apparent that various modifications can be madewithout departing from the spirit and scope of the disclosure.Accordingly, it is not intended that the disclosure be limited, exceptas by the appended claims.

What is claimed is:
 1. An expandable intervertebral implant comprising:a front wall; a back wall spaced apart from the front wall; two sidewalls connecting the front wall and the back wall at their respectiveends, the front wall, back wall and the two side walls defining a space;a bottom face; a top face; at least one engagement member with anengagement surface configured to engage an end plate of a vertebralbody; a first adjusting element and a second adjusting element which aresupported by a first support member and a second support member,respectively, and which cooperate with the respective support membersuch that the engagement member is reciprocally movable between a firstend position and a second end position wherein the engagement surface atleast partially projects outwardly beyond the bottom face or the topface, the second end position being different from the first endposition; wherein the first and the second support members are coupledby a coupling mechanism; and wherein an axis of movement of the firstsupport member and an axis of movement of the second support memberdefine an angle which is different from zero.
 2. The intervertebralimplant of claim 1, wherein the coupling mechanism transfers therotation of the first support member to the second support member. 3.The intervertebral implant of claim 1, wherein the coupling mechanismcomprises a rotational coupling.
 4. The intervertebral implant of claim1, wherein the coupling mechanism comprises a flexible tube.
 5. Theintervertebral implant of claim 1, wherein the coupling mechanismcomprises one of a bevel gear drive, a tube made of rigid material withbending zones and a flexible tube drive.
 6. The intervertebral implantof claim 1, wherein the support members are formed as first and secondthreaded spindles having opposite thread pitch.
 7. The intervertebralimplant of claim 1, wherein the adjusting elements are wedge members,said wedge members operating to move the engagement member.
 8. Theintervertebral implant according to claim 6, wherein the adjustingelements are formed as wedge members and one end of the first treadedspindle being rotationally supported in the first side wall, one end ofthe second threaded spindle being rotationally supported in the secondside wall and the other ends being rotationally coupled to each other;and wherein the two wedge members are supported within the space in sucha manner, that, upon rotation of the first or the second threadedspindle in one direction a distance between the wedge members decreasesand upon rotation of the threaded spindle in an opposite direction thedistance between the wedge members increases, and said wedge membersoperate to move the engagement element.
 9. The intervertebral implantaccording to claim 6, wherein the engagement member has two inclinedsurfaces on a side opposite to said engagement surface and wherein thewedge members engage the inclined surfaces.
 10. The intervertebralimplant according to claim 1, wherein at least the front wall or theback wall is curved.
 11. The intervertebral implant according to claim1, wherein the walls of the implant are curved in such a way that thecontour of the space which is formed by the walls is substantiallybanana-shaped.
 12. The intervertebral implant according to claim 1,wherein the engagement surface of the engagement member comprises anengagement structure for penetration into an adjacent bone material. 13.An intervertebral implant according to claim 1, further comprising astop that limits the outward movement of the engagement member.
 14. Theintervertebral implant according to claim 1, comprising two engagementmembers movable in opposite directions.
 15. The intervertebral implantaccording to claim 1, wherein the first support member and the secondsupport member are each supported in one of said walls.
 16. Theintervertebral implant according to claim 1, wherein the adjustingelements are each guided by two of the walls.
 17. The intervertebralimplant according to claim 7, wherein the engagement member has twoinclined surfaces on a side opposite to said engagement surface andwherein the wedge members engage the inclined surfaces.
 18. Theintervertebral implant according to claim 1, wherein the first supportmember is rotatable about the axis of movement of the first supportmember and the second support member is rotatable about the axis ofmovement of the second support member.
 19. A method of replacing anintervertebral disk with an intervertebral implant comprising a frontwall, a back wall spaced apart from the front wall, two side wallsconnecting the front wall and the back wall at their respective ends,the front wall, back wall and the two side walls defining a space, theimplant further comprising a bottom face, a top face, at least oneengagement member with an engagement surface configured to engage an endplate of a vertebral body, a first adjusting element and a secondadjusting element which are supported by a first support member and asecond support member, respectively, and which cooperate with therespective support member such that the engagement member isreciprocally movable between a first end position and a second endposition wherein the engagement surface at least partially projectsoutwardly beyond the bottom face or the top face, the second endposition being different from the first end position, wherein the firstand the second support members are coupled by a coupling mechanism, andwherein an axis of movement of the first support member and an axis ofmovement of the second support member define an angle which is differentfrom zero, the method comprising: inserting the intervertebral implantbetween two vertebral bodies; and moving the at least one engagementmember from the first end position to an implanted position between thefirst end position and the second end position; wherein the engagementsurface of the at least one engagement member engages the end plate ofone of the vertebral bodies in the implanted position of the engagementmember.
 20. The method of claim 19, where moving the at least oneengagement member comprises rotating the first support member about theaxis of movement of the first support member and rotating the secondsupport member about the axis of movement of the second support member.